1. Field of the Invention
The present invention relates to a turret punch press, and more particularly to a turret punch press having a characteristic structure for mounting a die to a lower turret.
2. Description of the Related Arts
Conventionally, an upper turret mounting a plurality of punches in a freely selecting manner and a lower turret mounting a plurality of dies in a freely selecting manner have the same diameter, and generally, the desired punch and die are synchronously rotated and indexed to a processing position and the punch is hit so as to perform a punching process to the work.
In the turret punch press of this kind, the upper turret and the lower turret are disposed such as to be freely rotated and indexed in a synchronous manner. A plurality of punches are mounted to the upper turret, and a plurality of dies are mounted to the lower turret.
The die is mounted to the lower turret through a die holder in such a manner as to oppose to the punch mounted to the upper turret. The die holder is provided with an upper die holder mounting the die and a lower die holder for mounting the upper die holder to the lower turret. The lower die holder is fixed to the lower turret by means of a mounting bolt. Accordingly, the die is fitted into the upper die holder, and the upper die holder is mounted to the lower die holder by means of a corner bolt. Accordingly, the die will be mounted to the lower turret.
However, in the turret punch press of this kind, since a gap between a lower surface of the upper turret and an upper surface of the upper die holder mounted to the lower turret is small, it is necessary to remove and take out the upper die holder from the lower die holder so as to replace the die at a time of replacing the die.
Further, at a time of setting the die, the die is inserted into the upper die holder and the upper die holder is mounted to the lower die holder. At this time, there has been a problem that a mounting position of the upper die holder is scattered, so that a core of the die is off-set with respect to a core of the punch every time when the die is replaced.
Accordingly, as described in Italian Utility Model No. 4745B/89, Japanese Patent 2659679 (Japanese Patent Unexamined Publication No. 7-136724) or Japanese Patent Unexamined Publication No. 3-60822, a turret punch press which is structured such that an outer diameter of the lower turret is made greater than an outer diameter of the upper turret is suggested. In the turret punch press mentioned above, since a part of the lower turret is exposed outside the upper turret, the die fitted into the lower turret through a faucet type die holder can be easily replaced only by pulling out to an immediately upward direction, thereby solving the problem mentioned above.
However, in the turret punch press which is structured to make the outer diameter of the lower turret mentioned above greater than the outer diameter of the upper turret, there is a problem that an alignment with respect to the punch can not be adjusted at a time of replacing the die. Accordingly, the upper turret and the lower turret have to be strictly processed at a time of manufacturing the turret punch press, so that a productivity is deteriorated.
Further, when the punch and the die are worn away due to a long time use, a clearance between the punch and the die becomes uneven, so that a great burr is locally generated at a punched portion in the work, whereby a problem of becoming impossible to be used is generated.